EP1564852B9 - Pumping unit for an optical laser-amplifier. - Google Patents

Pumping unit for an optical laser-amplifier. Download PDF

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Publication number
EP1564852B9
EP1564852B9 EP20050100894 EP05100894A EP1564852B9 EP 1564852 B9 EP1564852 B9 EP 1564852B9 EP 20050100894 EP20050100894 EP 20050100894 EP 05100894 A EP05100894 A EP 05100894A EP 1564852 B9 EP1564852 B9 EP 1564852B9
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European Patent Office
Prior art keywords
pumping
face
amplifying
media
main
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EP20050100894
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German (de)
French (fr)
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EP1564852A1 (en
EP1564852B1 (en
Inventor
Eric Durand
Christophe Derycke
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Thales SA
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Thales SA
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/0602—Crystal lasers or glass lasers
    • H01S3/0606—Crystal lasers or glass lasers with polygonal cross-section, e.g. slab, prism
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/0941—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
    • H01S3/0071—Beam steering, e.g. whereby a mirror outside the cavity is present to change the beam direction
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/08072—Thermal lensing or thermally induced birefringence; Compensation thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/08095—Zig-zag travelling beam through the active medium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/23—Arrangements of two or more lasers not provided for in groups H01S3/02 - H01S3/22, e.g. tandem arrangements of separate active media
    • H01S3/2308—Amplifier arrangements, e.g. MOPA
    • H01S3/2316—Cascaded amplifiers

Definitions

  • the present invention relates to a pumping head for optical amplification laser effect and a laser amplifier and a laser oscillator equipped with such a pumping head.
  • pumping heads with optical amplifying media or "slabs" according to the English expression, formed of a block generally of substantially parallelepiped shape, made of a Ytrium Garnet and Aluminum (or YAG) crystal laser material, doped with rare earth ions.
  • the figure 1 represents an example of such an amplifying medium 1. It comprises in known manner a block of doped laser material, substantially parallelepipedic, with an input face 10, an exit face 11, four lateral faces 121 to 124, two faces of which main lateral vis-à-vis substantially parallel, noted 121 and 122 on the figure 1 .
  • pumping means 2 arranged on one of said main faces (121), referred to in the following main pumping face, and intended to form in the amplifying medium a pumping zone 3 forming a band which extends from said main face of pumping up to the face vis-à-vis, and wherein an optical beam to be amplified 4, incident on the input face, is intended to propagate to the output face.
  • the main axis of propagation of the beam (called the longitudinal axis) is noted z, and x and y are the axes orthogonal to the longitudinal axis z, located in directions respectively transverse to the pumping zone and parallel to it.
  • a cooling block 5 is provided for cooling the face vis-à-vis the main pumping face.
  • the Figures 2A and 2B represent schematically the pumping energy distribution in the amplifying medium, seen in two longitudinal sections of the amplifying medium, respectively the longitudinal section AA in the yz plane ( Figure 2A ) and the longitudinal section BB in the plane xz ( Figure 2B ).
  • the pumping flux F P is absorbed by the amplifying medium and makes it possible to excite the atoms of the material at the origin of the laser effect. However, as the efficiency of the pumping process remains low, part of the luminous flux is dissipated inside the medium in the form of heat.
  • the pumping light flux absorbed by the amplifying medium is maximum close to the pumping surface 121, resulting in a thermal gradient between the main pumping face and the facing face.
  • T ° opposite represented on the Figure 2A by an arrow referenced T °.
  • the distribution of the pumping energy has a quasi-Gaussian shape with a maximum in the center, and an attenuation on the edges, as it appears on the Figure 2B .
  • the thermal gradients created in the two directions x and y orthogonal to the main axis z of propagation of the beam generate distortions of the beam after passing through the amplifying medium.
  • the US Patent 4,730,324 discloses a pumping head with two substantially identical amplifying media, of collinear longitudinal axes, these two amplifying media being rotated relative to each other by 90 ° in order to compensate for the astigmatism effect.
  • the two amplifying media remain aligned, a particular prism, called Dove prism, being positioned between the two amplifying media to rotate the beam.
  • Dove prism a particular prism
  • This second solution is more satisfactory because it avoids the mechanical and hydraulic problems inherent in the relative positioning at 90 ° of the two amplifying media.
  • the prism of Dove causes a depolarization of the beam that is necessary to compensate by interposing an additional optical element, such as a phase plate.
  • the invention proposes a pumping head with two amplifying media for compensating the transverse thermal gradient, without additional optical element, and in which the relative positioning of each of the amplifying media with respect to the longitudinal axis is preserved.
  • the longitudinal axes of the amplifying media are no longer maintained collinear, an optical reflection device with two plane mirrors receiving the beam amplified by the first amplifying medium and reflecting it towards the second amplifying medium, making it possible to turn the beam around its axis of propagation, without introducing depolarization.
  • the figure 3 represents a first embodiment of a pumping head according to the invention. It comprises a first and a second substantially identical amplifying medium 1, 1 'of the type of those represented on FIG. figure 1 , each formed of a block with an inlet face (10, 10 '), an outlet face (11, 11') and four lateral faces, of which two main faces facing substantially parallel, respectively 121 , 122 and 121 ', 122'.
  • the block forming the amplifying medium is substantially parallelepipedal, with the parallel or substantially trapezoidal input and output faces with the non-parallel input and output faces, as on FIG. figure 3 .
  • the amplifying media 1, 1 ' are for example formed with a YAG (Yttrium garnet aluminum) type crystal, pumped by rare earth ions, such as for example Erbium, Holmium, Neodymium or Thulium.
  • rare earth ions such as for example Erbium, Holmium, Neodymium or Thulium.
  • Other materials can of course be used to produce amplifying media, such as phosphate or silicate glasses, and generally any laser medium having a high refractive index.
  • the pumping head further comprises first and second pumping means amplifying media (not shown on the figure 3 ), according to one of the main faces of each of the media, called the main pumping face (respectively 121 and 121 ').
  • the pumping means are intended to emit a pumping flow F P making it possible to form in each amplifying medium a pumping zone (no represented on the figure 3 but similar to the pumping zone 3 of Figures 1, 2A and 2B ), extending from the main pumping face to the opposite face, and in which an optical beam to be amplified, incident on the input face, is intended to propagate.
  • the refractive index of the amplifying medium is generally high relative to that of the materials in contact with the main faces, so that a beam incident on the input side of an amplifying medium with an angle of incidence given zig-zag propagates to the exit face, by total reflections on the main faces.
  • This zigzag propagation makes it possible to compensate for the distortion effects due to the thermal gradient in the direction parallel to the direction of the pumping flow F P.
  • the pumping means comprise laser diodes or stacks of laser diodes substantially aligned along the main pumping surface, between the input and output faces of the amplifying medium.
  • Other means of pumping can be used, such as flashlights, arches, or filament lamps.
  • the pumping head may comprise cooling devices for the amplifying media (not shown in FIG. figure 3 ), in particular for cooling the face vis-à-vis the main face of pumping.
  • each cooling device of each of the amplifying media comprises a cooling block of the face opposite the main pumping surface, of the type of the cooling block 5 shown in FIG. figure 1 , with, advantageously, an intermediate layer of index given between the face to be cooled and the cooling block to ensure total reflection on said face during zig-zag propagation of the beam to be amplified.
  • each cooling device then comprising a cooling block for each of the main faces.
  • the amplifying media 1, 1 ' are arranged relative to one another so that their main faces are located in parallel planes, the pumping zones being non-coplanar.
  • the optical beam to be amplified 4 is identified by its different parts relative to the positions of the amplifying media.
  • the portion of the incident beam on the first amplifying medium 41, the portion of the emerging beam of the first amplifying medium and incident on the second amplifying medium, and 42 the portion of the emerging beam of the second amplifying medium are noted.
  • the pumping head comprises an optical reflection device 6 with at least two plane mirrors 61, 62 arranged in such a way that the beam 41 emerges from the first amplifying medium undergoes a rotation of 90 ° about its axis of propagation before to enter the pumping zone of the second amplifying medium.
  • the optical device 6 of reflection of the pumping head according to the invention makes it possible to compensate without introducing additional optical element, and in particular of element acting on the phase, the phase distortion of the optical beam introduced by the thermal gradients of the first amplifying medium, by simple propagation in the second amplifying medium, substantially identical to the first.
  • the axis z 1 of propagation of the emergent beam 41 of the first amplifier is in a given first plane ( ⁇ 1 ), and the two plane mirrors 61, 62 are arranged in such a way that the axis of propagation Z 2 of the beam after reflection on the two mirrors is in a second plane ( ⁇ 2 ) parallel to the first, the z axis 2 being perpendicular to the direction of the propagation axis z 1 before reflection.
  • the two amplifying media 1, 1 ' are arranged in two distinct parallel planes, so that the pumping zones are substantially perpendicular to each other.
  • the beam 41 coming from the first amplifying medium propagates in the plane ⁇ 1 , is reflected on the mirror 61 in a vertical plane, then returns in a plane ⁇ 2 parallel to the initial plane after reflection on the plane mirror 62.
  • the change planes makes it possible to turn the beam 41 by 90 ° without introducing depolarization of the incident beam when the latter is polarized linearly.
  • the figure 4 represents a second variant of a pumping head according to the invention, substantially similar to the pumping head shown in FIG. figure 3 but in which the optical reflection device comprises a third reflecting mirror 63 for reducing the axis of propagation z 3 of the beam after reflection on the three mirrors in a direction substantially parallel to the direction of the propagation axis z 1 before reflection, but not aligned, the two amplifying media 1, 1 'then being arranged in two distinct parallel planes with the pumping zones substantially parallel to each other. 'other.
  • the change of planes made thanks to the reflection mirrors 61 and 62 makes it possible to rotate the beam 41 by 90 °.
  • This variant has the additional advantage, thanks to the third mirror 63, of reducing the bulk of the pumping head, in particular with respect to the devices of the prior art in which the amplifying media were necessarily arranged along collinear axes.
  • the invention further relates to a laser amplifier with one or more pump heads as described above, and for example represented on the figures 3 or 4 .
  • An incident beam in the amplifier is then intended to be amplified by each of the amplifying media of the pump head or heads.
  • the amplification is made by single passage in each of the amplifying media.
  • a multiple passage of the beam to be amplified is provided in the pumping zone of one or more of the amplifying media.
  • the invention also relates to a laser oscillator comprising an oscillating cavity closed by two mirrors with in the cavity, one or more pump heads as described above.
  • the oscillator may further comprise a Q-switch trigger.

Description

La présente invention concerne une tête de pompage pour amplification optique à effet laser ainsi qu'un amplificateur laser et un oscillateur laser équipé d'une telle tête de pompage.The present invention relates to a pumping head for optical amplification laser effect and a laser amplifier and a laser oscillator equipped with such a pumping head.

Dans le domaine des amplificateurs optiques à effet laser, et notamment pour la réalisation de lasers solides de forte puissance, il est connu d'utiliser des têtes de pompage avec des milieux amplificateurs optiques, ou "slabs" selon l'expression anglo-saxonne, formés d'un bloc généralement de forme sensiblement parallélépipédique, en matériau laser de type cristal de Grenat d'Ytrium et d'Aluminium (ou YAG), dopé par des ions terre rare.In the field of optical amplifiers with a laser effect, and especially for the production of solid lasers of high power, it is known to use pumping heads with optical amplifying media, or "slabs" according to the English expression, formed of a block generally of substantially parallelepiped shape, made of a Ytrium Garnet and Aluminum (or YAG) crystal laser material, doped with rare earth ions.

La figure 1 représente un exemple d'un tel milieu amplificateur 1. Il comprend de façon connue un bloc en matériau laser dopé, sensiblement parallélépipédique, avec une face d'entrée 10, une face de sortie 11, quatre faces latérales 121 à 124, dont deux faces latérales principales en vis-à-vis sensiblement parallèles, notées 121 et 122 sur la figure 1. Sur la figure 1, sont également représentés des moyens de pompage 2 agencés sur une desdites faces principales (121), appelée dans la suite face principale de pompage, et destinés à former dans le milieu amplificateur une zone de pompage 3 formant une bande qui s'étend de ladite face principale de pompage jusqu'à la face en vis-à-vis, et dans laquelle un faisceau optique à amplifier 4, incident sur la face d'entrée, est destiné à se propager jusqu'à la face de sortie. On note z l'axe principal de propagation du faisceau (appelé axe longitudinal), et x et y les axes orthogonaux à l'axe longitudinal z, situés dans des directions respectivement transverse à la zone de pompage et parallèle à celle-ci. Un bloc de refroidissement 5 est prévu pour le refroidissement de la face en vis-à-vis de la face principale de pompage.The figure 1 represents an example of such an amplifying medium 1. It comprises in known manner a block of doped laser material, substantially parallelepipedic, with an input face 10, an exit face 11, four lateral faces 121 to 124, two faces of which main lateral vis-à-vis substantially parallel, noted 121 and 122 on the figure 1 . On the figure 1 are also represented pumping means 2 arranged on one of said main faces (121), referred to in the following main pumping face, and intended to form in the amplifying medium a pumping zone 3 forming a band which extends from said main face of pumping up to the face vis-à-vis, and wherein an optical beam to be amplified 4, incident on the input face, is intended to propagate to the output face. The main axis of propagation of the beam (called the longitudinal axis) is noted z, and x and y are the axes orthogonal to the longitudinal axis z, located in directions respectively transverse to the pumping zone and parallel to it. A cooling block 5 is provided for cooling the face vis-à-vis the main pumping face.

Les figures 2A et 2B représentent de façon schématique la répartition d'énergie de pompage dans le milieu amplificateur, vue selon deux coupes longitudinales du milieu amplificateur, respectivement la coupe longitudinale AA dans le plan yz (figure 2A) et la coupe longitudinale BB dans le plan xz (figure 2B). Le flux de pompage FP est absorbé par le milieu amplificateur et permet d'exciter les atomes du matériau à l'origine de l'effet laser. Cependant, l'efficacité du processus de pompage restant faible, une partie du flux lumineux est dissipé à l'intérieur du milieu sous forme de chaleur. Dans la direction y parallèle à la zone de pompage 3, le flux lumineux de pompage absorbé par le milieu amplificateur est maximal à proximité de la face de pompage 121, résultant en un gradient thermique entre la face principale de pompage et la face en vis-à-vis représenté sur la figure 2A par une flèche référencée T°. Dans la direction x transverse à la zone de pompage, la répartition de l'énergie de pompage présente une forme quasi-gaussienne avec un maximum au centre, et une atténuation sur les bords, comme cela apparaît sur la figure 2B. Les gradients thermiques créés dans les deux directions x et y orthogonales à l'axe principal z de propagation du faisceau génèrent des distorsions du faisceau après passage dans le milieu amplificateur.The Figures 2A and 2B represent schematically the pumping energy distribution in the amplifying medium, seen in two longitudinal sections of the amplifying medium, respectively the longitudinal section AA in the yz plane ( Figure 2A ) and the longitudinal section BB in the plane xz ( Figure 2B ). The pumping flux F P is absorbed by the amplifying medium and makes it possible to excite the atoms of the material at the origin of the laser effect. However, as the efficiency of the pumping process remains low, part of the luminous flux is dissipated inside the medium in the form of heat. In the direction y parallel to the pumping zone 3, the pumping light flux absorbed by the amplifying medium is maximum close to the pumping surface 121, resulting in a thermal gradient between the main pumping face and the facing face. opposite represented on the Figure 2A by an arrow referenced T °. In the x-direction transverse to the pumping zone, the distribution of the pumping energy has a quasi-Gaussian shape with a maximum in the center, and an attenuation on the edges, as it appears on the Figure 2B . The thermal gradients created in the two directions x and y orthogonal to the main axis z of propagation of the beam generate distortions of the beam after passing through the amplifying medium.

Pour compenser l'effet du gradient thermique dans la direction y parallèle à la zone de pompage, il est connu de faire propager le faisceau lumineux en zig-zag dans la zone de pompage, en lui faisant subir une succession de réflexions totales sur les faces principales en vis-à-vis 121, 122, comme cela apparaît sur la figure 1. Le trajet en zig-zag permet de compenser l'effet du gradient thermique dans cette direction. Par contre, ces gradients ne sont pas compensés dans la direction transverse x, ce qui provoque un fort astigmatisme du faisceau après traversée du milieu amplificateur.To compensate for the effect of the thermal gradient in the y direction parallel to the pumping zone, it is known to propagate the zig-zag light beam in the pumping zone, subjecting it to a succession of total reflections on the faces. the main ones vis-à-vis 121, 122, as appears on the figure 1 . The zig-zag path compensates for the effect of the thermal gradient in this direction. On the other hand, these gradients are not compensated in the transverse direction x, which causes a strong astigmatism of the beam after passing through the amplifying medium.

Pour remédier à cet effet, de nombreuses méthodes ont été envisagées dans lesquelles on agit sur le refroidissement des faces latérales. Ces procédés permettent de réduire les gradients de température sans pour autant les compenser et sont compliqués à mettre en oeuvre.To remedy this effect, many methods have been envisaged in which it acts on the cooling side faces. These methods make it possible to reduce the temperature gradients without compensating for them and are complicated to implement.

Le brevet US 4,730,324 décrit une tête de pompage à deux milieux amplificateurs sensiblement identiques, d'axes longitudinaux colinéaires, ces deux milieux amplificateurs étant tournés l'un par rapport à l'autre de 90° afin de compenser l'effet d'astigmatisme. Selon une variante, les deux milieux amplificateurs restent alignés, un prisme particulier, appelé prisme de Dove, étant positionné entre les deux milieux amplificateurs pour faire tourner le faisceau. Cette deuxième solution est plus satisfaisante car elle permet d'éviter les problèmes mécaniques et hydrauliques inhérents au positionnement relatif à 90° des deux milieux amplificateurs. Cependant, le prisme de Dove entraîne une dépolarisation du faisceau qu'il est nécessaire de compenser en interposant un élément optique supplémentaire, comme une lame de phase.The US Patent 4,730,324 discloses a pumping head with two substantially identical amplifying media, of collinear longitudinal axes, these two amplifying media being rotated relative to each other by 90 ° in order to compensate for the astigmatism effect. According to a variant, the two amplifying media remain aligned, a particular prism, called Dove prism, being positioned between the two amplifying media to rotate the beam. This second solution is more satisfactory because it avoids the mechanical and hydraulic problems inherent in the relative positioning at 90 ° of the two amplifying media. However, the prism of Dove causes a depolarization of the beam that is necessary to compensate by interposing an additional optical element, such as a phase plate.

L'invention propose une tête de pompage à deux milieux amplificateurs pour compenser le gradient thermique transverse, sans élément optique supplémentaire, et dans laquelle le positionnement relatif de chacun des milieux amplificateurs par rapport à l'axe longitudinal est conservé. Pour cela les axes longitudinaux des milieux amplificateurs ne sont plus maintenus colinéaires, un dispositif optique de réflexion avec deux miroirs plans recevant le faisceau amplifié par le premier milieu amplificateur et le réfléchissant vers le second milieu amplificateur, permettant de faire tourner le faisceau autour de son axe de propagation, sans introduire de dépolarisation.The invention proposes a pumping head with two amplifying media for compensating the transverse thermal gradient, without additional optical element, and in which the relative positioning of each of the amplifying media with respect to the longitudinal axis is preserved. For this purpose, the longitudinal axes of the amplifying media are no longer maintained collinear, an optical reflection device with two plane mirrors receiving the beam amplified by the first amplifying medium and reflecting it towards the second amplifying medium, making it possible to turn the beam around its axis of propagation, without introducing depolarization.

Plus précisément, l'invention propose une tête de pompage pour amplificateur optique à effet laser, comprenant :

  • un premier et un second milieux amplificateurs sensiblement identiques, formés chacun d'un bloc avec une face d'entrée, une face de sortie et quatre faces latérales, dont deux faces principales en vis-à-vis sensiblement parallèles,
  • des premier et second moyens de pompage desdits milieux amplificateurs selon l'une desdites faces principales de chacun desdits milieux, appelée face principale de pompage, les moyens de pompage étant destinés à former dans chacun des milieux amplificateurs une zone de pompage dans laquelle un faisceau optique à amplifier, incident sur la face d'entrée, est destiné à se propager en zig-zag jusqu'à la face de sortie, par réflexion totale sur lesdites faces principales,
la tête de pompage étant caractérisée en ce que les milieux amplificateurs sont disposés l'un par rapport à l'autre de telle sorte que leurs faces principales soient situées dans des plans parallèles, les zones de pompage étant non coplanaires, et en ce qu'elle comprend un dispositif optique de réflexion avec au moins deux miroirs plans agencés de telle sorte qu'un faisceau émergent du premier milieu amplificateur selon un axe de propagation donné subisse une rotation de 90° autour dudit axe de propagation avant de pénétrer dans la zone de pompage du second milieu amplificateur.More specifically, the invention proposes a pumping head for a laser-effect optical amplifier, comprising:
  • a first and a second substantially identical amplifying medium, each formed of a block with an inlet face, an exit face and four lateral faces, of which two main faces are vis-à-vis substantially parallel,
  • first and second pumping means of said amplifying media according to one of said main faces of each of said media, called the main pumping surface, the pumping means being intended to form in each amplifying medium a pumping zone in which an optical beam to amplify, incident on the input face, is intended to propagate zig-zag to the exit face, by total reflection on said main faces,
the pumping head being characterized in that the amplifying media are arranged relative to each other so that their main faces are located in parallel planes, the pumping zones being non-coplanar, and in that it comprises an optical reflection device with at least two plane mirrors arranged in such a way that a beam emerging from the first amplifying medium along a given axis of propagation undergoes a rotation of 90 ° about said axis of propagation before entering the zone of pumping the second amplifying medium.

D'autres avantages et caractéristiques apparaîtront plus clairement à la lecture de la description qui suit, illustrée par les figures annexées qui représentent :

  • La figure 1, un schéma illustrant un milieu amplificateur, ou slab (déjà décrite);
  • Les figures 2A et 2B, des schémas illustrant la répartition de l'énergie de pompage dans un milieu amplificateur du type de celui de la figure 1 (déjà décrite);
  • La figure 3, un exemple de réalisation d'une tête de pompage selon l'invention dans un premier exemple de réalisation;
  • La figure 4, un exemple de réalisation d'une tête de pompage selon l'invention dans un second exemple de réalisation.
Other advantages and characteristics will appear more clearly on reading the description which follows, illustrated by the appended figures which represent:
  • The figure 1 a diagram illustrating an amplifying medium, or slab (already described);
  • The Figures 2A and 2B , diagrams illustrating the distribution of the pumping energy in an amplifying medium of the type of that of the figure 1 (already described);
  • The figure 3 , an exemplary embodiment of a pumping head according to the invention in a first embodiment;
  • The figure 4 , an exemplary embodiment of a pumping head according to the invention in a second embodiment.

Sur ces figures les éléments identiques sont référencés par les mêmes repères.In these figures, the identical elements are referenced by the same references.

La figure 3 représente un premier exemple de réalisation d'une tête de pompage selon l'invention. Elle comprend un premier et un second milieux amplificateurs 1, 1' sensiblement identiques, du type de ceux représentés sur la figure 1, formés chacun d'un bloc avec une face d'entrée (10, 10'), une face de sortie (11, 11') et quatre faces latérales, dont deux faces principales en vis-à-vis sensiblement parallèles, respectivement 121, 122 et 121', 122'. Le bloc formant le milieu amplificateur est par exemple sensiblement parallélépipédique, avec les faces d'entrée et de sortie parallèles ou sensiblement trapézoïdal avec les faces d'entrée et de sortie non parallèles, comme sur la figure 3.The figure 3 represents a first embodiment of a pumping head according to the invention. It comprises a first and a second substantially identical amplifying medium 1, 1 'of the type of those represented on FIG. figure 1 , each formed of a block with an inlet face (10, 10 '), an outlet face (11, 11') and four lateral faces, of which two main faces facing substantially parallel, respectively 121 , 122 and 121 ', 122'. For example, the block forming the amplifying medium is substantially parallelepipedal, with the parallel or substantially trapezoidal input and output faces with the non-parallel input and output faces, as on FIG. figure 3 .

Les milieux amplificateurs 1, 1' sont par exemple formés avec un cristal de type YAG (Grenat d'Yttrium et d'Aluminium), pompé par des ions terres rares, comme par exemple l'Erbium, l'Holmium, le Néodyme ou le Thulium. D'autres matériaux peuvent bien entendu être utilisés pour réaliser les milieux amplificateurs, tels que les verres phosphate ou silicate, et de façon générale tout milieu laser ayant un indice de réfraction élevé.The amplifying media 1, 1 'are for example formed with a YAG (Yttrium garnet aluminum) type crystal, pumped by rare earth ions, such as for example Erbium, Holmium, Neodymium or Thulium. Other materials can of course be used to produce amplifying media, such as phosphate or silicate glasses, and generally any laser medium having a high refractive index.

La tête de pompage comprend en outre des premier et second moyens de pompage des milieux amplificateurs (non représentés sur la figure 3), selon l'une des faces principales de chacun des milieux, appelée face principale de pompage (respectivement 121 et 121'). Les moyens de pompage sont destinés à émettre un flux de pompage FP permettant de former dans chacun des milieux amplificateurs une zone de pompage (non représentée sur la figure 3 mais similaire à la zone de pompage 3 des figures 1, 2A et 2B), s'étendant de la face principale de pompage à la face en vis-à-vis, et dans laquelle un faisceau optique à amplifier, incident sur la face d'entrée, est destiné à se propager. L'indice de réfraction du milieu amplificateur est en général élevé par rapport à celui des matériaux en contact avec les faces principales, de telle sorte qu'un faisceau incident sur la face d'entrée d'un milieu amplificateur avec un angle d'incidence donné se propage en zig-zag jusqu'à la face de sortie, par réflexions totales sur les faces principales. Cette propagation en zigzag permet de compenser les effets de distorsion dus au gradient thermique dans la direction parallèle à la direction du flux de pompage FP.The pumping head further comprises first and second pumping means amplifying media (not shown on the figure 3 ), according to one of the main faces of each of the media, called the main pumping face (respectively 121 and 121 '). The pumping means are intended to emit a pumping flow F P making it possible to form in each amplifying medium a pumping zone (no represented on the figure 3 but similar to the pumping zone 3 of Figures 1, 2A and 2B ), extending from the main pumping face to the opposite face, and in which an optical beam to be amplified, incident on the input face, is intended to propagate. The refractive index of the amplifying medium is generally high relative to that of the materials in contact with the main faces, so that a beam incident on the input side of an amplifying medium with an angle of incidence given zig-zag propagates to the exit face, by total reflections on the main faces. This zigzag propagation makes it possible to compensate for the distortion effects due to the thermal gradient in the direction parallel to the direction of the pumping flow F P.

Avantageusement, les moyens de pompage comprennent des diodes laser ou des empilements de diodes laser sensiblement alignés le long de la face principale de pompage, entre les faces d'entrée et de sortie du milieu amplificateur. D'autres moyens de pompage peuvent être utilisés, type lampes à flashs, à arcs, ou lampes à filament. De façon classique, la tête de pompage peut comprendre des dispositifs de refroidissement des milieux amplificateurs (non représentés sur la figure 3), en particulier pour le refroidissement de la face en vis-à-vis de la face principale de pompage. Par exemple, chaque dispositif de refroidissement de chacun des milieux amplificateurs comprend un bloc de refroidissement de la face en vis-à-vis de la face principale de pompage, du type du bloc de refroidissement 5 représenté sur la figure 1, avec, de façon avantageuse, une couche intermédiaire d'indice donné entre la face à refroidir et le bloc de refroidissement pour assurer la réflexion totale sur ladite face lors de la propagation en zig-zag du faisceau à amplifier.Advantageously, the pumping means comprise laser diodes or stacks of laser diodes substantially aligned along the main pumping surface, between the input and output faces of the amplifying medium. Other means of pumping can be used, such as flashlights, arches, or filament lamps. In a conventional manner, the pumping head may comprise cooling devices for the amplifying media (not shown in FIG. figure 3 ), in particular for cooling the face vis-à-vis the main face of pumping. For example, each cooling device of each of the amplifying media comprises a cooling block of the face opposite the main pumping surface, of the type of the cooling block 5 shown in FIG. figure 1 , with, advantageously, an intermediate layer of index given between the face to be cooled and the cooling block to ensure total reflection on said face during zig-zag propagation of the beam to be amplified.

Bien entendu, d'autres variantes sont possibles pour la mise en oeuvre des moyens de pompage. Par exemple, il est possible de prévoir pour chacun des milieux amplificateurs des moyens de pompage de la face en vis-à-vis de la face principale de pompage, chaque dispositif de refroidissement comprenant alors un bloc de refroidissement pour chacune des faces principales.Of course, other variants are possible for the implementation of the pumping means. For example, it is possible to provide for each amplifying medium pumping means of the face vis-à-vis the main pumping face, each cooling device then comprising a cooling block for each of the main faces.

Selon l'invention, les milieux amplificateurs 1, 1' sont disposés l'un par rapport à l'autre de telle sorte que leurs faces principales soient situées dans des plans parallèles, les zones de pompage étant non coplanaires. Sur la figure 3, le faisceau optique à amplifier 4 est repéré par ses différentes parties, relativement aux positions des milieux amplificateurs. Ainsi on note 40 la partie du faisceau incidente sur le premier milieu amplificateur, 41, la partie du faisceau émergente du premier milieu amplificateur, et incidente sur le second milieu amplificateur, et 42, la partie du faisceau émergente du second milieu amplificateur. La tête de pompage comprend selon l'invention un dispositif optique de réflexion 6 avec au moins deux miroirs plans 61, 62 agencés de telle sorte que le faisceau 41 émergent du premier milieu amplificateur subisse une rotation de 90° autour de son axe de propagation avant de pénétrer dans la zone de pompage du second milieu amplificateur. Le dispositif optique 6 de réflexion de la tête de pompage selon l'invention permet de compenser sans introduire d'élément optique supplémentaire, et notamment d'élément agissant sur la phase, la distorsion de phase du faisceau optique introduite par les gradients thermiques du premier milieu amplificateur, par simple propagation dans le second milieu amplificateur, sensiblement identique au premier.According to the invention, the amplifying media 1, 1 'are arranged relative to one another so that their main faces are located in parallel planes, the pumping zones being non-coplanar. Sure the figure 3 , the optical beam to be amplified 4 is identified by its different parts relative to the positions of the amplifying media. Thus, the portion of the incident beam on the first amplifying medium 41, the portion of the emerging beam of the first amplifying medium and incident on the second amplifying medium, and 42 the portion of the emerging beam of the second amplifying medium are noted. According to the invention, the pumping head comprises an optical reflection device 6 with at least two plane mirrors 61, 62 arranged in such a way that the beam 41 emerges from the first amplifying medium undergoes a rotation of 90 ° about its axis of propagation before to enter the pumping zone of the second amplifying medium. The optical device 6 of reflection of the pumping head according to the invention makes it possible to compensate without introducing additional optical element, and in particular of element acting on the phase, the phase distortion of the optical beam introduced by the thermal gradients of the first amplifying medium, by simple propagation in the second amplifying medium, substantially identical to the first.

Dans l'exemple de la figure 3, l'axe z1 de propagation du faisceau émergent 41 du premier amplificateur est dans un premier plan donné (π1), et les deux miroirs plans 61, 62 sont agencés de telle sorte que l'axe de propagation Z2 du faisceau après réflexion sur les deux miroirs se trouve dans un second plan (π2) parallèle au premier, l'axe z2 étant perpendiculaire à la direction de l'axe de propagation z1 avant réflexion. Selon une première variante, illustrée sur la figure 3, les deux milieux amplificateurs 1, 1' sont disposés dans deux plans parallèles distincts, de telle sorte que les zones de pompage se trouvent sensiblement perpendiculaires l'une à l'autre. Ainsi, le faisceau 41 issu du premier milieu amplificateur se propage dans le plan π1, se réfléchit sur le miroir 61 dans un plan vertical, puis revient dans un plan π2 parallèle au plan initial après réflexion sur le miroir plan 62. Le changement de plans permet de faire tourner le faisceau 41 de 90° sans introduire de dépolarisation du faisceau incident lorsque celui-ci est polarisé linéairement.In the example of the figure 3 the axis z 1 of propagation of the emergent beam 41 of the first amplifier is in a given first plane (π 1 ), and the two plane mirrors 61, 62 are arranged in such a way that the axis of propagation Z 2 of the beam after reflection on the two mirrors is in a second plane (π 2 ) parallel to the first, the z axis 2 being perpendicular to the direction of the propagation axis z 1 before reflection. According to a first variant, illustrated on the figure 3 the two amplifying media 1, 1 'are arranged in two distinct parallel planes, so that the pumping zones are substantially perpendicular to each other. Thus, the beam 41 coming from the first amplifying medium propagates in the plane π 1 , is reflected on the mirror 61 in a vertical plane, then returns in a plane π 2 parallel to the initial plane after reflection on the plane mirror 62. The change planes makes it possible to turn the beam 41 by 90 ° without introducing depolarization of the incident beam when the latter is polarized linearly.

La figure 4 représente une seconde variante d'une tête de pompage selon l'invention, sensiblement similaire à la tête de pompage représentée sur la figure 3 mais dans laquelle le dispositif optique de réflexion comprend un troisième miroir de renvoi 63 permettant de ramener l'axe de propagation z3 du faisceau après réflexion sur les trois miroirs dans une direction sensiblement parallèle à la direction de l'axe de propagation z1 avant réflexion, mais non alignée, les deux milieux amplificateurs 1, 1' étant alors disposés dans deux plans parallèles distincts avec les zones de pompage sensiblement parallèles l'une à l'autre. Comme dans l'exemple de la figure 3, le changement de plans effectué grâce aux miroirs de réflexion 61 et 62 permet de faire tourner le faisceau 41 de 90°. Cette variante présente l'avantage supplémentaire, grâce au troisième miroir 63, de réduire l'encombrement de la tête de pompage, notamment par rapport aux dispositifs de l'art antérieur dans lesquels les milieux amplificateurs étaient nécessairement disposés selon des axes colinéaires.The figure 4 represents a second variant of a pumping head according to the invention, substantially similar to the pumping head shown in FIG. figure 3 but in which the optical reflection device comprises a third reflecting mirror 63 for reducing the axis of propagation z 3 of the beam after reflection on the three mirrors in a direction substantially parallel to the direction of the propagation axis z 1 before reflection, but not aligned, the two amplifying media 1, 1 'then being arranged in two distinct parallel planes with the pumping zones substantially parallel to each other. 'other. As in the example of figure 3 , the change of planes made thanks to the reflection mirrors 61 and 62 makes it possible to rotate the beam 41 by 90 °. This variant has the additional advantage, thanks to the third mirror 63, of reducing the bulk of the pumping head, in particular with respect to the devices of the prior art in which the amplifying media were necessarily arranged along collinear axes.

L'invention concerne en outre un amplificateur laser avec une ou plusieurs têtes de pompage telles que décrites précédemment, et par exemple représentées sur les figures 3 ou 4. Un faisceau incident dans l'amplificateur est alors destiné à être amplifié par chacun des milieux amplificateurs de la ou des têtes de pompage.The invention further relates to a laser amplifier with one or more pump heads as described above, and for example represented on the figures 3 or 4 . An incident beam in the amplifier is then intended to be amplified by each of the amplifying media of the pump head or heads.

Selon une variante, l'amplification est faite par passage unique dans chacun des milieux amplificateurs. Selon une seconde variante, un passage multiple du faisceau à amplifier est prévu dans la zone de pompage d'un ou plusieurs des milieux amplificateurs.According to one variant, the amplification is made by single passage in each of the amplifying media. According to a second variant, a multiple passage of the beam to be amplified is provided in the pumping zone of one or more of the amplifying media.

L'invention concerne aussi un oscillateur laser comprenant une cavité oscillante fermée par deux miroirs avec dans la cavité, une ou plusieurs têtes de pompage telles que décrites précédemment. L'oscillateur peut comprendre en outre un déclencheur de type Q-Switch.The invention also relates to a laser oscillator comprising an oscillating cavity closed by two mirrors with in the cavity, one or more pump heads as described above. The oscillator may further comprise a Q-switch trigger.

Claims (14)

  1. Pump head for laser optical amplifier comprising
    - a first and a second amplifying media (1, 1') that are substantially identical, each formed of a block with an input face (10, 10'), an output face (11, 11') and four lateral faces, including two substantially parallel opposite main faces (121, 122, 121', 122'),
    - first and second means (2) for pumping the said amplifying media along one of the said main faces of each of the said media, called the main pumping face (121, 121'), the pumping means being designed to form in each of the amplifying media a pumping zone (3) forming a band which extends from the said main pumping face up to the opposite face in which an optical beam to be amplified (4), incident on the input face, is designed to be propagated in a zig zag up to the output face, by total reflection of the said main faces,
    the amplifying media (1, 1') being placed one relative to the other such that their main faces are situated in distinct parallel planes,
    the pump head being characterized in that the pumping zones are not coplanar and in that it comprises a reflective optical device (6) with two flat mirrors (61, 62) arranged such that the beam (41) emerging from the first amplifying medium along a given propagation axis (z1) sustains a 90° rotation by means of the said mirrors about said propagation axis before entering the pumping zone of the second amplifying medium and in that the direction of the propagation axis (z2) of said beam after reflection on the two mirrors is perpendicular to the direction of the propagation axis (z1) of the beam before reflection.
  2. Pump head according to Claim 1, in which the two amplifying media are placed in two distinct parallel planes, such that the pumping zones are substantially perpendicular to one another.
  3. Pump head for laser optical amplifier comprising
    - a first and a second amplifying medium (1, 1') that are substantially identical, each formed of a block with an input face (10, 10'), an output face (11, 11') and four lateral faces, including two substantially parallel opposite main faces (121, 122, 121', 122'),
    - first and second means (2) for pumping the said amplifying media along one of the said main faces of each of the said media, called the main pumping face (121, 121'), the pumping means being designed to form in each of the amplifying media a pumping zone (3) forming a band which extends from the said main pumping face up to the opposite face in which an optical beam to be amplified (4), incident on the input face, is designed to be propagated in a zig zag up to the output face, by total reflection of the said main faces,
    the amplifying media (1, 1') being placed one relative to the other such that their main faces are situated in distinct parallel planes,
    the pump head being characterized in that the pumping zones are not coplanar,
    and in that it comprises a reflective optical device (6) with three flat mirrors (61, 62, 63) arranged such that the beam (41) emerging from the first amplifier (1) being contained in a first plane (Π1), is contained in a second plane (Π2) parallel to the first after reflection on two first mirrors (61, 62) and after reflection on the third mirror (63), the beam (41) emerging from the first amplifying medium along a given propagation axis (z1) undergoes a 90° rotation about the said propagation axis by means of the first two mirrors (61, 62) before being reflected by the third mirror (63), and that the direction of the propagation axis (z2) of the said beam after reflection on the first two mirrors (61, 62) is perpendicular to the direction of the propagation axis (z1) of the beam before reflection and the propagation axis (z3) of the beam after reflection on the third mirror (63) is in a direction substantially parallel to the direction of the propagation axis (z1) before reflection,
    the two amplifying media being placed in two distinct parallel planes, the pumping zones being substantially parallel with one another.
  4. Pump head according to one of the preceding claims, in which the first and second pumping means comprise laser diodes or stacks of laser diodes substantially aligned along the main pumping face, between the input and output faces of the amplifying medium.
  5. Pump head according to one of the preceding claims, also comprising first and second devices for cooling the amplifying media (5), notably for cooling the face opposite to the main pumping face.
  6. Pump head according to Claim 5, in which each cooling device comprises a block for cooling the said face opposite to the main pumping face, with an intermediate layer of given index between the said face and the cooling block in order to ensure total reflection on the said face during the zig zag propagation of the beam to be amplified.
  7. Pump head according to one of the preceding claims, also comprising for each of the amplifying media means for pumping the face opposite to the main pumping face, each cooling device comprising a cooling block for each of the main faces.
  8. Pump head according to one of the preceding claims, in which the block forming the amplifying medium is substantially parallelepipedal, with the input and output faces parallel or substantially trapezoidal with the input and output faces not parallel.
  9. Pump head according to one of the preceding claims, in which the amplifying medium is formed with a crystal of the YAG type, pumped by rare-earth ions.
  10. Pump head according to Claim 9, in which the rare-earth ions are erbium, holmium, neodymium or thulium.
  11. Laser amplifier comprising one or more pump heads according to one of the preceding claims, an incident beam in the amplifier being designed to be amplified by each of the amplifying media of the pump head(s).
  12. Laser amplifier according to Claim 11, in which the amplification in one or more of the said amplifying media is carried out by a multiple passage of the beam to be amplified in the pumping zone of the said media.
  13. Laser oscillator comprising an oscillating cavity closed by two mirrors and in the said cavity, one or more pump heads according to one of Claims 1 to 10.
  14. Laser oscillator according to Claim 13, also comprising a trigger of the Q-Switch type.
EP20050100894 2004-02-10 2005-02-09 Pumping unit for an optical laser-amplifier. Expired - Fee Related EP1564852B9 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR0401284 2004-02-10
FR0401284A FR2866161B1 (en) 2004-02-10 2004-02-10 PUMPING HEAD FOR OPTICAL AMPLIFIER WITH LASER EFFECT

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EP1564852B1 EP1564852B1 (en) 2008-08-06
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WO1987004870A1 (en) * 1986-01-30 1987-08-13 Advanced Lasers Ltd. A compact slab laser oscillator-amplifier system
JPH06268292A (en) * 1993-03-10 1994-09-22 Univ Osaka Solid laser oscillator
US6178040B1 (en) * 1998-06-25 2001-01-23 Trw Inc. Laser with two orthogonal zig-zag slab gain media for optical phase distortion compensation

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EP1564852A1 (en) 2005-08-17
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DE602005008653D1 (en) 2008-09-18
EP1564852B1 (en) 2008-08-06

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